The zoo was wonderful when we were there many years ago... there was also a wonderful botanical garden, but I don't remember where? close to the zoo perhaps? Peter Raven who co-wrote several Biology books (books I used over many years of teaching upper level HS Science) was at Washington University, and I THINK he was involved in developing/maintaining the gardens? (not sure about that...)
The Busch family farm is close to St. Louis too... this is where they keep their horse teams... a friend reported a great time there...
Have fun!!!